Sheet forming system for a machine for producing a multilayer fibrous web

Abstract

A sheet-forming system includes a separating wedge with a separating wedge protrusion in a range of 0.05 to 3.0 of the largest single gap width of at least two nozzle chambers. The separating wedge includes two separating wedge areas, each having one separating wedge angle, an upstream separating wedge starting area and a downstream separating wedge ending area. The two separating wedge angles assume different angles. The separating wedge starting angle of the upstream separating wedge initial area assumes a greater angle than the separating wedge ending angle of the downstream separating wedge end area. At least one separating wedge surface is a nonplanar transitional area between the two separating wedge areas. The fibrous material suspension free jet formed from at least two fibrous material suspension streams has a free jet length of 100 to 500 mm. The forming roll has a diameter of 1,200 to 2,500 mm.

1. A sheet forming system for a machine for producing a multilayer fibrous web from at least two fibrous stock suspensions, the multilayer fibrous web being one of a multilayer paper web and a multilayer cardboard web, said sheet forming system comprising:
 a multilayer headbox with a headbox nozzle which includes at least one separating wedge and at least two converging nozzle chambers extending over a width of the machine and separated from one another by said at least one separating wedge, said at least two converging nozzle chambers including a first nozzle chamber and a second nozzle chamber, said first nozzle chamber carrying a first fibrous stock suspension of the at least two fibrous stock suspensions in a form of a first fibrous stock suspension stream during an operation of said multilayer headbox, said second nozzle chamber carrying a second fibrous stock suspension of the at least two fibrous stock suspensions in a form of a second fibrous stock suspension stream during said operation of said multilayer headbox, said first nozzle chamber being equipped with a first upstream feed device and a first downstream outlet gap extending over said width and including a first gap width, said second nozzle chamber being equipped with a second upstream feed device and a second downstream outlet gap extending over said width and including a second gap width, said first and second nozzle chambers each being an outer nozzle chamber, said first nozzle chamber having a first outside wall on an outside of said first nozzle chamber, said second nozzle chamber having a second outside wall on an outside of said second nozzle chamber, said at least one separating wedge having a first separating wedge surface and a second separating wedge surface, said first separating wedge surface being in contact with said first fibrous stock suspension stream which is adjacent said first separating wedge surface during said operation of said multilayer headbox, said second separating wedge surface being in contact with said second fibrous stock suspension stream which is adjacent said second separating wedge surface during said operation of said multilayer headbox, said at least one separating wedge arranged in said headbox nozzle having a separating wedge protrusion in a range of 0.5 to 3.0 times a largest individual gap width of said at least two converging nozzle chambers, said at least one separating wedge including two separating wedge areas which are an upstream separating wedge starting area and a downstream separating wedge end area, said upstream separating wedge starting area having a separating wedge starting angle, said downstream separating wedge end area having a second separating wedge end angle, said separating wedge starting and end angles of said two separating wedge areas having different angular values, said separating wedge starting angle of said upstream separating wedge starting area having a greater angular value than said separating wedge end angle of said downstream separating wedge end area, at least one of said first separating wedge surface and said second separating wedge surface respectively including a non-planar transition area between said two separating wedge areas of said at least one separating wedge; and 
 one gap former which is located immediately downstream from said multilayer headbox and which has a continuous revolving first wire and a continuous revolving second wire, said gap former further including a forming roll and a breast roll, said forming roll including a circumferential area and being an open forming roll, said breast roll including a circumferential area, said first wire running over said circumferential area of said forming roll, said second wire running over said circumferential area of said breast roll and then running onto said first wire in an area of the sheet forming system of said forming roll, thus forming a wedge shaped stock inlet gap which immediately receives said first and second fibrous stock suspension streams emerging from said headbox nozzle of said multilayer headbox as one common fibrous stock suspension free jet having a free jet length, said first and second wires with the at least two fibrous stock suspensions therebetween forming a twin wire zone at least in a plurality of sections, said common fibrous stock suspension free jet which includes at least said first and second fibrous stock suspension streams having a free jet length in a range of 100 mm to 500 mm, said open forming roll having a diameter in a range of 1,200 mm to 2,500 mm. 
 
     
     
       2. The sheet forming system according to  claim 1 , wherein said separating wedge protrusion is in a range of 0.1 to 2.0 times said largest individual gap width of said at least two converging nozzle chambers. 
     
     
       3. The sheet forming system according to  claim 1 , wherein said separating wedge protrusion is in a range of 0.2 to 1.5 times said largest individual gap width of said at least two converging nozzle chambers. 
     
     
       4. The sheet forming system according to  claim 1 , wherein said free jet length is in a range of 125 mm to 400 mm and said diameter is in a range of 1,300 mm to 2,400 mm. 
     
     
       5. The sheet forming system according to  claim 1 , wherein said free jet length is in a range of 150 mm to 300 mm and said diameter is in a range of 1,500 mm to 2,200 mm. 
     
     
       6. The sheet forming system according to  claim 1 , wherein said headbox nozzle is a baffle-free headbox nozzle, said at least one separating wedge located in said baffle-free headbox nozzle having a separating wedge protrusion in a range of 0.05 to 1.0 times said largest individual gap width of said at least two converging nozzle chambers. 
     
     
       7. The sheet forming system according to  claim 1 , wherein said headbox nozzle is a baffle-free headbox nozzle, said at least one separating wedge located in said baffle-free headbox nozzle having a separating wedge protrusion in a range of 0.1 to 0.95 times said largest individual gap width of said at least two converging nozzle chambers. 
     
     
       8. The sheet forming system according to  claim 1 , wherein said headbox nozzle is a baffle-free headbox nozzle, said at least one separating wedge located in said baffle-free headbox nozzle having a separating wedge protrusion in a range of 0.2 to 0.90 times said largest individual gap width of said at least two converging nozzle chambers. 
     
     
       9. The sheet forming system according to  claim 1 , further including, located on at least one of said first outside wall and said second outside wall of said headbox nozzle, one adjustable baffle with a baffle immersion depth, said at least one separating wedge located in said headbox nozzle having a separating wedge protrusion in a range of 0.5 to ≦3.0 times said largest individual gap width of said at least two converging nozzle chambers. 
     
     
       10. The sheet forming system according to  claim 1 , further including, located on at least one of said first outside wall and said second outside wall of said headbox nozzle, one adjustable baffle with a baffle immersion depth, said at least one separating wedge located in said headbox nozzle having a separating wedge protrusion in a range of 0.6 to ≦2.0 times said largest individual gap width of said at least two converging nozzle chambers. 
     
     
       11. The sheet forming system according to  claim 1 , further including, located on at least one of said first outside wall and said second outside wall of said headbox nozzle, one adjustable baffle with a baffle immersion depth, said at least one separating wedge located in said headbox nozzle having a separating wedge protrusion in a range of 0.7 to 1.5 times said largest individual gap width of said at least two converging nozzle chambers. 
     
     
       12. The sheet forming system according to  claim 1 , wherein said first separating wedge surface includes thereon a first said non-planar transition area between said two separating wedge areas of said at least one separating wedge, said second separating wedge surface including thereon a second said non-planar transition area between said two separating wedge areas of said at least one separating wedge. 
     
     
       13. The sheet forming system according to  claim 1 , wherein said at least one separating wedge includes an upstream separating wedge retainer, at least said upstream separating wedge starting area of said at least one separating wedge being aligned symmetrically with one straight line extending through said upstream separating wedge retainer. 
     
     
       14. The sheet forming system according to  claim 13 , wherein said at least one separating wedge includes an upstream separating wedge retainer and a separating wedge tip, said upstream separating wedge starting area of said at least one separating wedge and said downstream separating wedge end area of said at least one separating wedge being aligned symmetrically to said straight line extending through said upstream separating wedge retainer of said at least one separating wedge so that said separating wedge tip of said at least one separating wedge is then positioned on said straight line extending through said upstream separating wedge retainer of said at least one separating wedge. 
     
     
       15. The sheet forming system according to  claim 1 , wherein said first separating wedge surface includes thereon said non-planar transition area between said two separating wedge areas of said at least one separating wedge, said second separating wedge surface including thereon a planar transition area between said two separating wedge areas of said at least one separating wedge. 
     
     
       16. The sheet forming system according to  claim 15 , wherein said at least one separating wedge includes an upstream separating wedge retainer, at least said upstream separating wedge starting area of said at least one separating wedge being aligned symmetrically with one straight line extending through said upstream separating wedge retainer of said at least one separating wedge. 
     
     
       17. The sheet forming system according to  claim 15 , wherein said at least one separating wedge includes an upstream separating wedge retainer, said upstream separating wedge starting area of said at least one separating wedge and said downstream separating wedge end area of said at least one separating wedge being aligned asymmetrically to a straight line extending through said upstream separating wedge retainer of said at least one separating wedge. 
     
     
       18. The sheet forming system according to  claim 1 , wherein said separating wedge starting angle of said upstream separating wedge starting area of said at least one separating wedge has an angular value in a range of 8° to 20°, and said separating wedge end angle of said downstream separating wedge end area of said at least one separating wedge has an angular value in a range of 1.5° to 8°. 
     
     
       19. The sheet forming system according to  claim 1 , wherein said separating wedge starting angle of said upstream separating wedge starting area of said at least one separating wedge has an angular value in a range of 10° to 15°, and said separating wedge end angle of said downstream separating wedge end area of said at least one separating wedge has an angular value in a range of 2.5° to 4.5°. 
     
     
       20. The sheet forming system according to  claim 1 , wherein said downstream separating wedge end area of said at least one separating wedge has a downstream separating wedge end length in a range of 10 mm to 100 mm. 
     
     
       21. The sheet forming system according to  claim 1 , wherein said downstream separating wedge end area of said at least one separating wedge has a downstream separating wedge end length in a range of 15 mm to 75 mm. 
     
     
       22. The sheet forming system according to  claim 1 , wherein said downstream separating wedge end area of said at least one separating wedge has a downstream separating wedge end length in a range of 25 mm to 50 mm. 
     
     
       23. The sheet forming system according to  claim 1 , wherein said downstream separating wedge end area of said at least one separating wedge protrudes beyond said first and second downstream outlet gaps of said headbox nozzle in a range of 10 mm to 25 mm. 
     
     
       24. The sheet forming system according to  claim 1 , wherein said open forming roll has an open area in a range of 60% to 99% of a total area of said open forming roll. 
     
     
       25. The sheet forming system according to  claim 1 , wherein said open forming roll has an open area in a range of 70% to 98% of a total area of said open forming roll. 
     
     
       26. The sheet forming system according to  claim 1 , wherein said open forming roll has an open area in a range of 80% to 96% of a total area of said open forming roll. 
     
     
       27. The sheet forming system according to  claim 1 , wherein said open forming roll has an area around which both said first and second wires, with the at least two fibrous stock suspensions therebetween, wrap with an angle of wrap in a range of 15° to 260°. 
     
     
       28. The sheet forming system according to  claim 1 , wherein said open forming roll has an area around which both said first and second wires, with the at least two fibrous stock suspensions therebetween, wrap with an angle of wrap in a range of 30° to 230°. 
     
     
       29. The sheet forming system according to  claim 1 , wherein said open forming roll has an area around which both said first and second wires, with the at least two fibrous stock suspensions therebetween, wrap with an angle of wrap in a range of 50° to 180°. 
     
     
       30. A machine to produce a multilayer fibrous web from at least two fibrous stock suspensions, the multilayer fibrous web being one of a multilayer paper web and a multilayer cardboard web, said machine comprising:
 at least one sheet forming system including:
 a multilayer headbox with a headbox nozzle which includes at least one separating wedge and at least two converging nozzle chambers extending over a width of the machine and separated from one another by said at least one separating wedge, said at least two converging nozzle chambers including a first nozzle chamber and a second nozzle chamber, said first nozzle chamber carrying a first fibrous stock suspension of the at least two fibrous stock suspensions in a form of a first fibrous stock suspension stream during an operation of said multilayer headbox, said second nozzle chamber carrying a second fibrous stock suspension of the at least two fibrous stock suspensions in a form of a second fibrous stock suspension stream during said operation of said multilayer headbox, said first nozzle chamber being equipped with a first upstream feed device and a first downstream outlet gap extending over said width and including a first gap width, said second nozzle chamber being equipped with a second upstream feed device and a second downstream outlet gap extending over said width and including a second gap width, said first and second nozzle chambers each being an outer nozzle chamber, said first nozzle chamber having a first outside wall on an outside of said first nozzle chamber, said second nozzle chamber having a second outside wall on an outside of said second nozzle chamber, said at least one separating wedge having a first separating wedge surface and a second separating wedge surface, said first separating wedge surface being in contact with said first fibrous stock suspension stream which is adjacent said first separating wedge surface during said operation of said multilayer headbox, said second separating wedge surface being in contact with said second fibrous stock suspension stream which is adjacent said second separating wedge surface during said operation of said multilayer headbox, said at least one separating wedge arranged in said headbox nozzle having a separating wedge protrusion in a range of 0.5 to 3.0 times a largest individual gap width of said at least two converging nozzle chambers, said at least one separating wedge including two separating wedge areas which are an upstream separating wedge starting area and a downstream separating wedge end area, said upstream separating wedge starting area having a separating wedge starting angle, said downstream separating wedge end area having a second separating wedge end angle, said separating wedge starting and end angles of said two separating wedge areas having different angular values, said separating wedge starting angle of said upstream separating wedge starting area having a greater angular value than said separating wedge end angle of said downstream separating wedge end area, at least one of said first separating wedge surface and said second separating wedge surface respectively including a non-planar transition area between said two separating wedge areas of said at least one separating wedge; and 
 one gap former which is located immediately downstream from said multilayer headbox and which has a continuous revolving first wire and a continuous revolving second wire, said gap former further including a forming roll and a breast roll, said forming roll including a circumferential area and being an open forming roll, said breast roll including a circumferential area, said first wire running over said circumferential area of said forming roll, said second wire running over said circumferential area of said breast roll and then running onto said first wire in an area of said sheet forming system of said forming roll, thus forming a wedge shaped stock inlet gap which immediately receives said first and second fibrous stock suspension streams emerging from said headbox nozzle of said multilayer headbox as one common fibrous stock suspension free jet having a free jet length, said first and second wires with the at least two fibrous stock suspensions therebetween forming a twin wire zone at least in a plurality of sections, said common fibrous stock suspension free jet which includes at least said first and second fibrous stock suspension streams having a free jet length in a range of 100 mm to 500 mm, said open forming roll having a diameter in a range of 1,200 mm to 2,500 mm.